Bring her into your house and take a good look at her - in the bathroom is probably best. Are there any blood feathers bleeding? If there's any bleeding use gauze or something without lint and apply pressure. Do you have Betadine or something similar? You can dilute it and dab it on broken skin.
Don't use peroxide - it kills healthy skin. Neosporin/triple antibiotic ointment is good to use once the wound is clean and dry. ummmmm...sorry for the multiple posts...stand by - I'm going to look at Storey's first aid section.
Cleanliness while healing is important...bites are a terrible thing and get infected easily. Sometimes bite wounds need to be squeezed a bit, and kept open to prevent internal buildup of pus, etc. With my dogs, when they get a bite wound I always wash my hands before getting near the wound, and a combination of a warm soapy rag to keep the area clean and kind of work puss out, then dab with another rag with 70% rubbing alcohol...I only do that for a few days and have had good luck with minor wounds healing on their own.
If the wounds start to smell bad or look abnormally swollen/pussy then take it to a vet!
I'm no expert but I would think (like mentioned above) keeping the duck inside, like in your bathtub with frequent water changes would reduce risk of infection from the wounds. I hope the best for you and the duck!
Yes that's right some light application of Neosporin does seem to help, but I wouldn't cake it in there, and clean and re-apply a couple times a day? Hopefully my advice is good...it's just what I have done and it worked out.
So much depends on the injuries, place, number, size.
Puncture wounds: How many? How deep? Where are they located? Do you have chickens? Ducks will pull out each others' feathers, but I'm not sure they can cause puncture wounds with their bills. But they can scratch up each other's backs with the little claws their feet. Mine decided to bum rush into a corner and tried to Yertle the Turtle each other, and the ones near the bottom lost back feather and had pin-prick bleeding dots. :(
This option is controversial - I used Blu Kote on their backs. Ducks can see in color, and I didn't want them to see red dots and think, "Looks tasty."
As far as her leg: if it's broken, you can splint it with tongue depressors, but I'd take care of wounds first.